The present invention generally relates to an internal combustion engine and more particularly, to an engine ignition arrangement having two ignition plugs for use in internal combustion engines.
Commonly, it has been well known that, if a swirl of an air-fuel mixture is arranged to be formed in a circumferential direction within a combustion chamber during an intake stroke of an engine so as to effect ignition with respect to such swirl, favorable ignition and combustion are achieved, even if the air-fuel mixture is lean.
Accordingly, there have conventionally been proposed several intake arrangements or intake constructions for forming a swirl of the air-fuel mixture during the intake stroke of internal combustion engines, for example, a combustion chamber construction in which a guide wall is provided to extend or project into the combustion chamber so as to cause the air-fuel mixture drawn from an intake port into the combustion chamber to swirl in the circumferential direction of the combustion chamber. Meanwhile, for the intake arrangements or intake constructions as described above, it has also been required to raise the compression ratio of the air-fuel mixture within the combustion chamber for the reduction of fuel cost and also for the improvement of combustion efficiency.
However, when the air-fuel mixture is highly compressed as described above, there are such disadvantages that, in addition to the tendency that the undesirable knocking phenomenon is liable to take place, if carbon adheres to a guide wall at the side of an exhaust port kept at high temperatures, an edge portion of such guide wall at the exhaust port side functions as a "heat point" different from a normal ignition plug for ignition, thus also resulting in the possibility of the knocking phenomenon. Particularly, in a large load and low speed rotation range of the engine, the generation of knocking is conspicuous, since the swirling speed of the intake air-fuel mixture is low, with a consequent delay of the flame propagation and low combustion speed, as compared with other operational ranges of the engine.